Circuit interrupting means



March 31, 1959 C. VH. BAKER CIRCUIT INTERRUPTING MEANS Filed July 25,1957 IVENTOR.

United States Patent O CIRCUIT INTERRUPTING MEANS Charles H. Baker,Arlington Heights, Ill., assignor to S&C Electric Company, Chicago,Ill., a corporation of Delaware Application July 2s, 1957, serial No.674,181

1o Claims. (Cl. 20o-120) This inventio-n relates, generally, to circuitinterrupting means and it has particular relation to fuse links. ltconstitutes an improvement over the fuse link construction shown inMcMahon Patent No. 2,586,171, issued February 19, 1952.

ln the patent above referred to a fuse link construction is disclosed inwhich an insulating and arc extinguishing sleeve is secured to one of apair of terminals of the fuse link which are interconnected by fusiblemeans. The sleeve was formed by convolutely wrapping a sheet of paper toform a liner, which was impregnated with an arc extinguishing material,and then surrounding the liner with a convolute Wrapping of pressuresensitive tape. The composite sleeve was adhesively secured to one ofthe fuse link terminals.

As pointed out in this patent, the fuse link construction was intendedfor use in expulsion fuse tubes the internal diameter of which rangedupwardly from 5/16. The maximum internal diameter of such fuse tube wasabout W16". The fuse link construction disclosed in the patentfunctioned satisfactorily for the interruption of low fault currents andhad a maximum interrupting capacity of the order of 200 to 300 amperes.Above this current range, rupture of the fuse link sleeve occurs andthen interruption of the current flow depends on the fuse tube withoutassistance from the sleeve. Thus, that fuse link did not always enablethe expulsion fuse tube or cutout to clear satisfactorily when the tubediameter was %6" or larger at currents above 300 amperes and normalfrequency recovery voltage corresponding to line circuit voltages of l2to 13.8 kv.

Since the advent of the fuse link construction of the McMahon patent,the available short circuit current on distribution circuits has becomehigher and higher. It has therefore become necessary to increase theinterrupting capacity of distribution cutouts. This was economicallyaccomplished in many cases by increasing the inside diameter or bore ofthe cutout fuse tube, thereby reducing the internal pressure developedat these higher short circuit currents and making interrupting possiblein a relatively light and inexpensive device.

Because of the increase in inside diameter of expulsion fuse tubes forcutouts and the reduced generation of deionizing gas from the walls ofthe tube itself by the heat of the arc at all current levels, there hasbeen an increase in the minimum current that can be interruptedsatisfactorily` in such a device without the assistance 0f the fuse tubelink sleeve. It will be seen that there is a range of fault currentsomewhat above the 200 to 300` ampere interrupting capacity of the fuselink of the McMahon patent which cannot be interrupted satisfactorily bymany expulsion fuse tubes that presently are being employed to meet theliioher interrupting requirement. The reason for this is the greaterinside diameter of such fuse tubes. The result has been that there isthe likelihood of relatively low current arcs persisting for severalcycles or even failure to clear the arc at all when the circuit shouldhave been interrupted promptly. A typical example of ICC such lowcurrent interrupting requirements is a secondary fault on a transformerwhich should be cleared promptly by the cutout connected in series withthe primary winding so as to prevent burn out of the windings of thetransformer. The transient recovery voltage in such case is relativelymore severe than occurs when a primary fault of high current magnitudeis interrupted while the generation of deionizing gas without the aid ofan efficient link sleeve would be at a low rate.

What is desired is an increase in the interrupting ability and strengthof the fuse link to extend its range upwardly in order to permit largerinternal diameters of expulsion fuse tubes while at the same timemaintaining the same external diameter of the fuse link sleeve so thatit still can be employed in existing expulsion fuse tubes having minimumdiameters of the order of 5/16 to W16. As pointed out in the McMahonpatent, for proper operation, there is a definite relationship betweenthe maximum interrupting ability of the fuse link sleeve and the minimuminterrupting ability 0f the expulsion fuse tube. Therefore, the solutionto the problem of obtaining higher current interrupting ability in afuse link sleeve lay not just in making it stronger to prevent burstingat the higher current, but this greater strength had to be obtainedwith,- out increase in the outside diameter.

The increase in bursting strength of the fuse link sleeve was not alonethe answer to the problem of increased interrupting capacity. In orderto realize this ability as the result of greater sleeve strength, it isnecessary that the sleeve be retained on the fuse link terminal to whichit is attached and to prevent it from being expelled from the cutouttube in the range of currents to be interrupted by the sleeve alone.While the sleeve of the McMahon patent would meet this requirement inthe range of current up to 200 amperes, it was found that a reinforcedstronger sleeve would not be retained on the terminal at higher current,such as to 800 amperes, which such a reinforced sleeve could interrupt.It was discovered that the innermost layer of paper of the liner for thefuse link sleeve remained firmly attached to the fuse link terminal butthat the remainder of the sleeve would be torn from this terminal bydelamination between the outer layers of the paper impregnated with arcextinguishing material. This delamination action took place in a rangefrom 400 to 800 amperes. In order to prevent such delamination andexpulsion of the sleeve from the cutout tube before it had anopportunity to extinguish the arc it was found that such undesirableaction could be prevented by providing a good bond between the layers ofthe convolutely wound paper at the end immediately surrounding the fuselink terminal. In accordance with this invention this was accomplishedby impregnating only that portionv of the paper forming the liner which.was to be coextensive with the fuse link terminal to which it wassecured with an adhesive of adequate strength while the paper was beingrolled into the tubular configuration. The adhesive impregnant used isof such character that it penetrates the interstices and fibres of thepaper and, upon drying of polymerization a substantially solidhomogeneous structure was attained. This solid end portion of thecompleted and reinforced fuse link sleeve then is attached to theterminal by a suitable adhesive. When such a construction is employeddelamination and loss of the fusev link sleeve does not occur within theinterrupting range ofv sleeve of a fuse link without increasing itsoutside diameter; to provide a construction that can resist endwiseforces between the sleeve and the terminal of the fuse link to which itis attached on blowing of the fusible means connected to the terminal inthe range of currents to be interrupted in the sleeve; and to limit theapplicaion of adhesive for that purpose to the line or of the sleeve andits convolute layers for bonding them together and securing the sleeveto the fuse link terminal substantially only to that portion that iscoextensive with the fuse'link terminal in order to avoid interferencewith the impregnation of the balance of the liner with arc extinguishingmaterial and subsequent liberation of water from the arc extinguishingmaterial when the liner is subjected to the heat of an arc incident tothe opening of a circuit on the occurrence of a fault therein.

Other objects of this invention will, in part, be obvious and in partappear hereinafter.

This invention is disclosed in the embodiment thereof shown in theaccompanying drawing and it comprises the features of construction,combination of elements and arrangement of parts that will beexemplified in the construction hereinafter set forth and the scope ofthe application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of thisinvention reference can be had to the following detailed description,taken together with the accompanying drawing, in which:

Figure 1 is a plan View of a paper sheet that is rolled convolutely inorder to form the liner for a fuse link sleeve;

Figure 2 is a plan view of a wrapper which is convolutely wound aroundthe liner in completing the formation of the fuse link sleeve; and

Figure 3 is a longitudinal sectional View of a fuse link employing thefuse link sleeve of the present invention.

Referring now to Figure 3 of the drawing, it will be observed that thereference character 10 designates, generally, a fuse link which istypical of the fuse links to which the present invention can be applied.The fuse link 10 includes relatively infusible terminals 11 and 12 whichare interconnected by fusible means that comprises a strain wire 13 anda fusible element 14. In some fuse links only the strain element 13 isemployed, the fusible element 14 being dispensed with. The upper end 15of the terminal 11 is threaded for receiving a removable button head 16with which a washer 17 cooperates to adapt the fuse link 10 for mountingin fuse tubes of varying diameters and to facilitate connection to oneterminal of the fuse tube. A stranded exible conductor 18 extends fromthe other terminal 12 for a length sufficient to extend out of the otherend of the expulsion fuse tube for connection to a second line terminal.

Surrounding the fusible means comprising the strain wire 13 and fusibleelement 14, secured to the terminal 11 and extending over the terminal12 is an insulating and arc extinguishing sleeve that is indicated,generally, at 21 in which are embodied the improvements of the presentinvention. It will be noted that the upper end of the sleeve 21 abuts aradial flange 22 forming a part of the terminal 11 and that it issecured to a sleeve attaching portion 23 intermediate the ends of theterminal 11 by an adhesive 24 which may be the adhesive disclosed in theMcMahon patent on the adhesive referred to hereinafter.

The sleeve 21 is provided with a liner 25 that is formed by convolutelyrolling a sheet 26, Figure 1, of alpha cellulose paper to form a tube.In accordance with this invention a layer of adhesive 27 is appliedalong one end of the sheet 26, as shown in Figure l, for a limitedextent which is substantially coextensive with the length of the sleeveattaching portion 23 of the terminal 11. The'adhesive 27, like theadhesive 24, can be an acetate adhesive, as disclosed in the McMahonpatent, or it can be a'water base emulsion of a synthetic resin which isof the rubber complex type. Whatever adhesive is used, it should be onewhich will completely penetrate and im-` pregnate the portion of thesheet 26 to which it is applied so that, when itis convolutely wound toprovide the liner 25, a homogeneous mass is provided which, in effect,is a solid in which the paper forms merely a ller. On blowing of thefusible means of a fuse link having the sleeve formed and attached asjust described, a blast of arc extinguishing vapor and gas is generatedby the ensuing arc. There is a relative endwise force applied to thesleeve 21 and terminal 11. Since there is no likelihood of delaminationof the liner 25' where it is secured to the sleeve attaching portion 23of the terminal 11, the sleeve 21 remains in place and holds the liner25 where the arc extinguishing material impregnated therein is availablefor arc extinguishing purposes until the arc is completely extinguished.Even though it were possible to impregnate the sheet 26 of paper withsome arc extinguishing material before winding it to form the liner 25,the application of a strong adhesive over the entire surface of thesheet 26 and between the layers of the same when it is convolutely woundwould interfere with the liberation of arc extinguishing gas from allbut the innermost convolution. If such a construction, as justdescribed, is not employed, the innermost convolution of the liner 25remains attached to the attaching portion 23 of he terminal 11 while theimmediately surrounding portion becomes detached and the principalportion of the sleeve 21 is expelled from the cutout tube before the arcis extinguished.

By applying the adhesive 27 only to a limited portion of the sheet 26and subsequently impregnating the balance of the sheet 26 with an arcextinguishing material, such as magnesium borate, boric acid, etc.,there is no interference with the evolution of arc extinguishing vaporsor gases from the convolute layers of the liner 25l when it is subjectedto the heat of the arc.

In order to withstand the greater bursting pressure within the liner 25incident to the use of the fuse link 10 in larger diameter expulsionfuse tubes than heretofore and interruption of currents below the valuesthat can be interrupted by the fuse tube itself, a wrapper 28 isconvolutely applied which has a higher strength than does the celluloseacetate wrapper for the sleeve shown in the McMahon patent. Asillustrated in Figure 2 of the drawing a sheet 29 of pressure sensitivetape is employed which preferably is a polyester resin film made fromethylene glycol and terephthalic acid that is sold in the' can be usedto reinforce the liner 25, such as the sheath of iiber that is shown inU. S. Patent No. 2,253,720 or the phenolic condensation product layershown in U.S. Patent No. 2,324,044.

Since certain changes can be made in the foregoing construction anddifferent embodiments of the invention can be made without departingfrom the spirit and scope thereof, it is intended that all matter shownin the ac-` companying drawing and described hereinbefore shall beinterpreted as illustrative and not in a limiting sense.

What is claimed as new is:

l. In a sleeve for attachment at one end to a terminal I of a fuse link,a liner of convolutely wound paper having a portion at said one endcoextensive with the portion of the terminal to which it is securedsubstantially completely impregnated with adhesive material havingrelatively high bonding strength and formed into a non-laminar section,the remaining portion of said liner being impregnated with arcextinguishing material different from said adhesive material and havingsubstantially less mechanical strength than said portion at said oneend.

2. A sleeve for attachment at one end to a terminal of a fuse linkcomprising, in combination, a liner of convolutely wound paper having aportion at said one end coextensive with the portion of the terminal towhich 1t is secured substantially completely impregnated with adhesivematerial and formed into a non-laminar section having relatively poorarc extinguishing characteristics, the remaining portion of said linerbeing impregnated with arc extinguishing material and providing saidremaining portion with relatively good arc extinguishingcharacteristics, and a wrapper overlying said liner and reinforcing thesame.

3. A sleeve for attachment at one end to a terminal of a fuse linkcomprising in combination, a liner of convolutely wound paper having aportion at said one end coextensive with the portion of the terminal towhich it is secured substantially lcompletely impregnated with adhesivematerial having relatively high bonding strength and formed into anon-laminar section, the remaining portion of said liner beingimpregnated with arc extinguishing material containing a substantialamount of water of crystallization, and a Wrapper convolutely wound onsaid liner and reinforcing the same.

4. A sleeve for attachment at one end to a terminal of a fuse linkcomprising, in combination, a liner of convolutely wound paper having aportion at said one end coextensive with the portion of the terminal towhich it is secured substantially completely impregnated with adhesivematerial and formed into a non-laminar section of relatively highmechanical strength, the remaining portion of said liner beingimpregnated with arc extinguishing material and having relatively lowmechanical strength, and a wrapper convolutely wound on said liner andreinforcing the same, said Wrapper being formed of polyester resin tilmpressure sensitive tape.

5. A replaceable fuse link comprising, in combination, a pair ofterminals interconnected by fusible means, one of said terminals havinga sleeve attaching portion intermediate its ends, and an arcextinguishing sleeve surrounding said fusible means, said sleeve beingadhesively secured to said sleeve attaching portion of said one terminaland extending over the other terminal, that portion of said sleeveimmediately surrounding said fusible means being formed by a convolutelywound paper sheet impregnated with an arc extinguishing material andhaving adhesive along one end coextensive substantially only with saidsleeve attaching portion of said one terminal and unitarily securing thejuxtaposed portions of the convolutions to hold them in place on saidsleeve attaching portion when the sleeve is subjected to an endwiseforce relative to said one terminal on blowing of said fusible means,that portion of said sleeve coextensive with said sleeve attachingportion of said terminal containing substantially none of said arcextinguishing material and having relatively high mechanical strengthand that portion of said sleeve carrying said arc extinguishing materialbeing relatively weak mechanically.

6. A replaceable fuse link comprising, in combination, a pair ofterminals interconnected by fusible means, one of said terminals havinga sleeve attaching portion intermediate its ends, and an arcextinguishing sleeve surrounding said fusible means, said sleeve beingadhesively secured to said sleeve attaching portion of said one terminaland extending over the other terminal, that portion of said sleeveimmediately surrounding said fusible means being formed by a convolutelywound paper sheet impregnated with an arc extinguishing material andbeing relatively weak mechanically and having adhesive along one endcoextensive substantially only with said sleeve attaching portions ofthe convolutions which are substantially free of said arc extinguishingmaterial and are relatively strong mechanically to hold them in place onsaid sleeve attaching portion when the sleeve is subjected to an endwiseforce relative to said one terminal on blowing of said fusible means,and a Wrapper overlying said liner and reinforcing the same.

7. A replaceable fuse link comprising, in combination, a pair ofterminals interconnected by fusible means, one of said terminals havinga sleeve attaching portion inter mediate its ends, and an arcextinguishing sleeve surrounding said fusible means, said sleeve beingadhesively secured to said sleeve attaching portion of said one terminaland extending over the other terminal, that portio-n of said sleeveimmediately surrounding said fusible means being formed by a convolutelywound paper sheet impregnated with an arc extinguishing materialcontaining a substantial amount of water of crystallization and havingadhesive along one end coextensive substantially only with said sleeveattaching portion of said one terminal and unitarily securing thejuxtaposed portions of the convolutions which are substantially free ofsaid arc extinguishing material to hold them in place on said sleeveattaching portion when the sleeve is subjected to an endwise forcerelative to said one terminal on blowing of said fusible means, and awrapper convolutely wound on said liner and reinforcing the same.

8. A replaceable fuse link comprising, in combination, a pair ofterminals interconnected by fusible means, one of said terminals havinga sleeve attaching portion intermediate its ends, and an arcextinguishing sleeve surrounding said fusible means, said sleeve beingadhesively secured to said sleeve attaching portion of said one terminaland extending over the other terminal, that portion of said sleeveimmediately surrounding said fusible means being formed by a convolutelywound paper sheet impregnated with an arc extinguishing ma terialcontaining a substantial amount of water of crystallization and beingrelatively weak mechanically and having adhesive along one endcoextensive substantially only with said sleeve attaching portion ofsaid one terminal and unitarily securing the juxtaposed portions of theconvolutions which are substantially free of said arc extinguishingmaterial and are relatively strong mechanically to hold them in place onsaid sleeve attaching portion when the sleeve is subjected to an endwiseforce relative to said one terminal on blowing of said fusible means,and a wrapper convolutely wound on said liner and reinforcing the same,said wrapper being formed of polyester resin lm pressure sensitive tape.

9. Method of making a liner for a fuse link which comprises: applying anadhesive along substantially the entire width at one end of a sheet ofpaper capable of absorbing the same, rolling the sheet convolutely toform a tube, and impregnating the portion of the tube exclusive of theportion carrying the adhesive with an arc extinguishing material.

10. Method of making a sleeve for a fuse link which comprises: applyingan adhesive along substantially the entire width at one end of a sheetof paper capable of absorbing the same, rolling the sheet convolutely toform a tube, impregnating the portion of the tube exclusive of theportion carrying the adhesive with an arc extinguishing material, andconvolutely winding a relatively high strength wrapper around said tube.

References Cited in the file of this patent UNITED STATES PATENTS2,328,825 McMahon Sept. 7, 1943 2,586,171 McMahon Feb. 19, 19522,740,016 Hughes Mar. 27, 1956

